The present invention relates to cooling systems for internal combustion engines.
The object of the present invention is that of providing a cooling system which has a high efficiency while having also a relatively simple and inexpensive structure. A further object is that of improving the efficiency of the engine, particularly by reducing the fuel consumption and the emission of noxious gases.
In view of achieving the above mentioned object, the invention provides an internal combustion engine comprising an engine block and a cylinder head, characterized in that said engine comprises a cooling system including:
a first circuit for cooling the cylinder head of the engine and a second circuit for cooling the engine block, which are completely separated from each other and make use of a first cooling fluid and a second cooling fluid respectively which are never mixed with each other, and
a liquid/liquid heat exchanger having two ways respectively interposed in the first circuit for cooling the cylinder head and in the second circuit for cooling the engine block, in order to transfer heat between said two fluids.
In the cooling system according to the invention, the two circuits for cooling the head and the engine block are completely separated from each other, so that the temperatures of the two circuits are kept separate from each other. Due to the difference of the temperatures of the first fluid for cooling the head and the second fluid for cooling the block, the block can be brought to the desired temperature very easily, by varying the flow of the second cooling fluid or the flow of the first cooling fluid through the heat exchanger, since the fluid circulating in the engine block is normally cooled by the fluid which circulates in the head by means of said liquid/liquid heat exchanger.
According to a further preferred feature of the invention, the cooling fluid used in the circuit for cooling the engine block is a high boiling point fluid, i.e. a fluid having a boiling temperature substantially greater than that of the water. Due to this feature, the temperature of the engine block can be increased greatly above 100xc2x0 C., such as up to 140xc2x0 C. This result is possible, since the circuit for cooling the engine block is relatively small, there is a relatively small quantity of fluid contained therein and also this circuit can be sealed and placed at a protected position, with no additional tubes arranged in the engine compartment outside the engine. A further advantage lies in that any damages to the radiator of the system for cooling the cylinder head, for example due to an accident, do not cause inconveniences to the circuit for cooling the engine block.
In the preferred embodiment of the invention, the second cooling fluid is the engine lubricating oil. In this case, the above mentioned second circuit is arranged so that the lubricating oil, after that it has cooled the engine block, is sent to the heat exchanger to be cooled there by the first fluid of the first circuit for cooling the cylinder head, whereupon the oil thus cooled is sent to the circuit for lubrication of the engine block and the cylinder head. Also in the case of this preferred embodiment, the pump which activates circulation of the fluid in the circuit for cooling the engine block may be the same pump of the engine lubricating circuit, driven by the internal combustion engine, or also provided with an associated driving electric motor.
The above mentioned heat exchanger is interposed in a conduit of the first cooling of the cylinder head. In a first solution, in this conduit the entire flow of the first cooling fluid flows. In a variant, only a part of the entire flow of the first cooling fluid flows in this conduit.
The first circuit for cooling the cylinder head comprises:
a radiator,
an output conduit for feeding the first cooling fluid from the cylinder head to the radiator,
a return conduit for returning the first cooling fluid from the radiator to the cylinder head,
a by-pass conduit by-passing the radiator,
a first flow regulating valve for regulating the flow fluid through the radiator, and
a pump for activating circulation of the first cooling fluid in the first circuit. This pump may be driven by the internal combustion engine, or may be provided with an associated driving adjustable electric motor. In one exemplary embodiment, within said by-pass conduit there is interposed a radiator for heating the motor-vehicle compartment.
In the above mentioned case in which the entire flow of the first cooling fluid flows through the heat exchanger, this heat exchanger is interposed within said output conduit of the first cooling circuit. In the case instead in which only a portion of the entire flow of the first cooling fluid flows through the heat exchanger, the heat exchanger is interposed in an auxiliary conduit which departs from said return conduit, in parallel to the cylinder head, a second flow regulating valve being interposed within this auxiliary conduit.
The flow regulating valve for regulating the flow of the first cooling fluid through the radiator of the circuit for cooling the cylinder head may be a conventional thermostatic valve or a proportional solenoid valve. Similarly, the above mentioned second flow regulating valve provided in said auxiliary conduit of the circuit for cooling the cylinder head, in the variant in which only a portion of the entire flow of the first fluid is used to cool the second fluid, may be proportional solenoid valve.
In the case of the preferred embodiment in which the second cooling fluid is the engine lubricating oil, the second circuit for cooling the engine block comprises a conduit for taking the lubricating oil from the engine oil pan and feeding heat to the engine block for cooling thereof, a conduit for feeding the oil after that it has cooled the engine block, to said heat exchanger, a conduit for returning the oil from the heat exchanger to the engine where the oil flows in the lubricating circuit and finally returns to the engine oil pump. In the return conduit of lubricating oil from the heat exchanger to the engine block there is interposed a filter. Also, preferably in parallel to this return conduit of the lubricating oil from the heat exchanger to the engine block there is arranged a by-pass conduit with an associated flow regulating valve by which a portion of the oil flow can be brought from the heat exchanger directly to the engine oil pump.
The engine according to the invention is further preferably provided with an electronic control unit which controls a plurality of electric devices associated to the cooling system, such as flow regulating proportional solenoid valves, and electric motors for driving pumps and the fan associated to the radiator, depending upon signals coming from sensors of various operating parameters of the engine, including a sensor of the temperature of the second fluid at the output from the heat exchanger and a sensor of the temperature of the metal body of the engine block.
Due to all the above indicated feature, the engine according to the invention is able to cool the cylinder head and the engine block efficiently and according to separate criteria. The use of the lubricating oil as a cooling fluid for the engine block enables the temperature of the lubricating oil to be kept under control at all speeds and loads of the engine. In particular, the temperature of the oil is always kept relatively high, so as to achieve a lower viscosity of the oil with resulting advantages of lower friction at the lubricated parts, lower power required for the oil pump and hence lower fuel consumption by the engine and lower emission of noxious gases at the exhaust. The higher operating temperature of the engine block enables the friction at the cylinder walls to be reduced and the combustion chamber to become more adiabatic, i.e. a greater quantity of heat to be converted into mechanical energy.